6533b82cfe1ef96bd128f387

RESEARCH PRODUCT

The tandem Diels-Alder reaction between acetylenedicarboxyaldehyde and N,N'-dipyrrolylmethane. An ab initio study of the molecular mechanisms

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Abstract An extensive exploration at RHF/3-21G and RHF/6-31G ∗ levels of the potential energy surface for the tandem cycloaddition of acetylenedicarboxyaldehyde to N,N'-dipyrrolylmethane allows us to characterize the reaction pathways and the associated stationary points. The formation of the pincer and/or domino adducts can be described as a stepwise mechanism. The first step, associated with an intermolecular [4 + 2] cycloaddition, is the rate determining step and an azanorbornadiene intermediate is obtained. The second step is an intramolecular [4 + 2] cycloaddition. The formation of the pincer adduct is the step which kinetically controls the global process, due to the low barrier height for the second intramolecular Diels-Alder step for the pincer channel. But the presence of a transition structure connecting the azanorbornadiene intermediates of the domino and pincer reaction pathways with an intrinsic low energy barrier associated to a configurational inversion on the nitrogen atom, allows the connection between both reactive channels. The Curtin-Hammett principle is operative in this reaction and by thermolysis the global process gives mainly the thermodynamically more stable domino product.